How Can I Trace My Dad's Biological Mother? He Has His Birth Certificate.

This does depend on where you live and how old your Grandmother would be now. You don't say whether or not your Dad was adopted.

If your dad has his birth certificate does it mention his father? Does he know his father at all.
One way of doing this is to look at the General Register Office Records to see if his mother ever married if she wasn't married at the time of his birth. You can do this either through Ancestry online or Ancestry UK or 1837 online.

You could look at old electoral registers for the area she lived in or subscribe to eroll online (UK) and search under her name. The problem is she may have married and changed her name.

I would be inclined to advise you to get a good, reputable family history researcher to help you - you'll see them advertised in Family History Magazines or search online for Family History researchers for the area you think she may have lived in .

Who brought your Father up? Can you ask them to tell you everything they know about his family?
Good Luck and I hope you find something helpful here.

If  you dad was born in  the U.K. a record exists of his mother, at the records office. You mention her as his biological mother, so was he adopted? If he was, there is still a way of finding her records.

In the town where his birth was registered, someone registerd it, and would be listed, a priest or organisation may have her records too. A local person, or your father's adoptive parents may know something. Adoptive records are now more open. After 100 years all records and the census for that year become public too.

I don't know how old your father is, or if his mother is still expected to be alive, if this is the case you could put an advertisement in the newspaper of the town, and state that your father, date of birth and place included, wants to get in touch with his long lost mother, include in it a box number to write to, and a phone number. Someone may contact you.

If she doesn't want to be found however, or is no longer alive you may be disappointed, but  it is worth a try, if all else fails.